Variations in Offshore Suspended Sediment Characteristics and Effects of Ocean Dynamics: The Case of Terrebonne Bay, Northern Gulf of Mexico

Marine dynamics plays an important role in understanding the variations in offshore suspended sediment distribution and transport direction. In this study, variations in total suspended sediment concentration (TSSC) over Terrebonne Bay in the northern Gulf of Mexico were investigated by using remote sensing technology in relation to ocean-atmospheric dynamics. The terrestrial rainfall/runoff and river discharge in the lower Mississippi River estuarine area during the study period played an important role in the surface TSSC distribution. In most cases, the wave period and wind speed affected TSSC and its distribution. There was an inverse relationship between TSSC and wave period, but wind speed exhibited a positive relationship with TSSC distribution; however, there was a slight delay. The southeast (onshore) wind accounted for 57.0% of the wind direction over the study area and played a major role in the control of the surface sediment concentration in Terrebonne Bay in July 2010. The onshore wind lifted the underlying sediment, increasing the TSSC at the sea surface. The maximum TSSC was 1056.47 mg/l in the southeast direction (96.75 degrees, onshore) on July 1. Other higher TSSCs were also observed in the southeast wind direction: 996.38, 820.55, and 605.27 mg/l with wind directions of 99.63, 127.33, and 120.17 degrees on 2, 5, and 6 July 2010, respectively. The correlation coefficients between TSSC and wave period and wind speed were 0.45 and 0.47, respectively (significant level of 99%). The sediment concentration in the coastal area was related to coastal erosion and river discharge. The sediment transport not only was related to the physical properties of the sediment, but also depended on the flow velocity. The wind-driven flow field is one of the main factors that drive sediment transport. The sediments in the estuary and bay have many similarities in their dynamic environment and development evolution. The study of the dynamic response of offshore sediments is a supplement to the theory of sediment transport in the estuary and coastal zones. The study of the relationship between ocean dynamics and sediment transport can provide a reference for the site selection of offshore engineering structures.